The Core Mechanic
Almost every static RPG uses dice and each uses them in a slightly different way. However, a well-written game will have only one way of using the dice for almost every type of action. Using entirely different dice-rolling practices for different kinds of task is arbitrary and confusing. This basic dice-rolling structure is the Core Mechanic. As a rule, the Core Mechanic will work in one of three ways.
Roll and Add – When an action is declared, the GM will provide a target number based upon the inherent challenge of the act. The player then rolls a standard number of dice and adds a number derived from his character's traits to the total. If the final score equals of beats the target number the effort succeeds. If it is less, the character fails.
Higher traits are an advantage because they produce higher scores. Circumstantial complications are reflected in positive or negative modifiers to the total scored.
A variation of this system uses the character's traits to dictate the number and size of dice rolled. Better traits produce better dice pools. In these cases, circumstantial modifiers will add or subtract dice.
Roll Under – When an action is attempted the player adds up his character's relevant traits. He then rolls a standard number of dice and attempts to score the trait total or below. Higher traits therefore produce better odds – but a maximum dice score is always going to fail. New players can find the need to roll low hard to adjust to, whilst players with dice-based superstitions (of which there are many) take care not to use their 'lucky' high-rolling dice in these systems.
Circumstantial complications are generally represented by adding to or subtracting from the figure rolled. Some games instead alter the number of dice rolled – which can make even minor impediments crippling.
Hits – The player rolls a number of dice based upon his traits. Each die is then separately compared to a target number (which may be constant or based on the difficulty of the act). Each die that equals or exceeds the target is a 'success' while the others are discarded. To actually succeed, the player must obtain a mandated number of 'successes'.
Circumstances may alter the number of dice rolled, the score required on each dice or the number of 'successes' required.
Having established the Core Mechanic, most games introduce the idea of contested rolls. When a character rolls to influence another, the target character often gets a dice roll to cancel it out. A well-written system will ensure that highly skilled characters usually overcome this resistance, but players feel better about bad things happening to their characters when they've failed a dice roll to prevent it.
Games where the number of dice rolled is fixed often include rules for Critical Successes and Botches. A Critical Success occurs when a player rolls the best possible score on the dice. Such a roll always succeeds even if the total would still be insufficient. More importantly, A Critical will prevail in any contested roll unless the opponent matches it.
A Botch occurs when the player rolls the worst possible result. Such a score always fails. A botch also grants the GM licence to throw in consequences that are improbable on a simple failure, such as friendly fire and equipment breakage.
Systems with variable dice pools rarely use these rules exactly as described above, but many use a modified form. A lesser version of the Critical is known as rolling up. A maximum score in these systems allows more dice to be rolled and added to the total. If these dice also score a maximum further dice are rolled and so on. Some games also roll down, with a minimum score causing a further roll to be subtracted from the result.
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Combat
Due to the relatively high risk of character death when fighting breaks out, even primarily non-combat games will also include expanded systems for adjudicating combat. Many such combat systems are extremely complex and offer a wide variety of tactical options. However, the real point of a Combat system is to introduce a small number of extra functions to the Core Mechanic.
Initiative – During a combat scene, everyone is trying to act as fast as possible. The first characters to act may succeed in striking down opponents before they can make a move, so it is extremely important to decide who goes first in a fair and reasonable manner. The Initiative rule is used for this and all other contests of reaction time.
Actions – Since everyone is trying to act, it follows that the person who moves first only has a small head start over their foes. It is therefore unfair if the person that wins initiative is permitted to perform a lengthy sequence of activities before passing turn. Combat turns take a small number of seconds and characters are further restricted to performing what counts as a single action before someone else gets a go. As a good rule of thumb a basic character can attack once with one action. Minor activities such as reloading, taking cover or even talking might also use up an action. Note that the list of actions in the combat rules are not exhaustive – this is still a role-playing game after all. However, you cannot perform more than one of the deeds described as a full action in a single move.
Damage – During combat, most actions consist of trying to kill a target with your weapon. Under the Core Mechanic, a completely successful opposed roll would indicate that this had happened. This makes for rather abrupt combat and can kill a player party very fast.
Most games limit a character to attempting to land a damaging hit. Once a hit has been established, the rules use a largely arbitrary damage system to determine how bad the injuries are. Some games factor the impressiveness of the attack roll into these calculations, but the most important factors are usually the weapon used and the target's toughness.
One hit kills are often possible but generally rare. This gives the players the chance to retreat from a losing fight and to start an easy one with confidence of survival. Nearly all systems have a buffer between 'incapacitated' and 'dead', allowing for close fights where the one or two victors left standing can proceed to heal the rest of the cast.
Some action games permit the player characters to absorb what appear to be absurd amounts of damage. This is needed to give 007-style characters the necessary degree of survivability, since RPG characters get hit a lot more often than protagonists in films and books. Non-disabling hits are sometimes regarded as near misses or exhausting parries, although this can create minor inconsistencies when it comes to healing.
The damage system is also used for non-combat injuries such as falling and medical treatment rules will generally be found in the same place.
Movement and ranges – The rules will usually define how far a character can move at a walk or run with a single action. These statistics are theoretically important because all attacks have a maximum effective range. Some systems go further and define these things in terms of squares on a scale map for miniatures.
This is because modern role-playing originally diverged from tabletop war-games. Early RPGs took place inside a 'dungeon' – a sequential Moria-inspired set of rooms each containing monsters, traps or other challenges for the players to encounter. The GM started the game with a complete map (usually concealed behind a cardboard screen) and the players gradually made their own version as they explored.
As the story-telling aspects of role-playing improved, the action increasingly took place outside of these contrived arenas. As the whole world opened up, it became less and less practical for the GM to maintain a scale map of the play area for tracking combatants. Modern GMs often keep only a vague track of the relative location of the characters and refer to these rules only when absolutely necessary.
That's it! This may seem like a lengthy pair of articles, but compare them to the length of any RPG rulebook. Different systems will include chapters on elements specific to their setting, such as vehicles, magic and sanity. However, by absorbing the above information you should be able to get to grips with almost any game in very little time. Good luck!
